A device for the continuous measurement of organic solvents in a liquid is known from the DE 31 26 648 C2. There, a semiconductor gas sensor is immersed into the liquid direct which, however, is separated from the liquid by means of a medium that is impervious to liquid. The liquid-impervious medium permits a diffusion of the dissolved free gases from the liquid to the semiconductor gas sensor so that the output signal of the latter is representative of the proportion of organic solvents in the liquid. But this device requires a direct immersion of the gas sensor into the liquid involving pertinent sealing problems. Besides, in the event of fluctuating liquid levels, a positional adjustment of the sensor may become necessary in order to ensure that the same is constantly immersed in the liquid but without being totally submerged in the latter. Moreover, the demands made with regard to the medium which is impervious to liquid and permits the gas to pass through are relatively high.
It is known furthermore from the DE 32 21 063 C3, to monitor a liquid by the addition of reagents for producing a chemical color reaction while use is made of a photometric measuring means. There, the reaction vessel is constructed in the form of a vertically disposed cylinder, into the underside of which the liquid to be monitored is introduced. In addition, supply lines terminate in the reaction vessel, via which it is possible to introduce various reagents in a controlled fashion.
The known apparatus requires somewhat more substantial constructional resources and exact dosing. Moreover, the flow of liquid has to be interrupted during a respective measurement so that no continuous monitoring of a liquid is possible.
The present invention is based upon the technical problem of providing a device and a method for the measurement of impurities in a liquid, more particularly water, which renders. possible a detection of even very low impurity concentrations with a relatively simple construction.